Haven't had any problems with RasterProp before and don't seem to have any lag in the FusTek IVA but, FusTek is the only thing I have that has the transparent windows. The lag is worst on launchpad spawn and teleport into orbit, dipping to the sub 1 fps range. Once the camera readjusts itself in orbit frame rate hits around 5fps. Vessels without windows seem to do well. Ive got a 560 Ti and 16GB ram so KSP usually runs fine.

Just tried it with the bare bones setup, it still behaves as Crampman stated. The buttons and windows shades work beautifully though. *EDIT* JSI is definitely the source of the ultra lag, remove it and everything is groovy (except none of the stuff that needs testing works).

At most only a ~30MB reduction in ram usage, hmm, still have Active Texture (aggressive) loaded after pairing down mods while troubleshooting "out of memory" problems. That may be the reason for the meager savings or part of the problem. *EDIT* Removing Active Texture Management (with the MLI Blanket removal of previous step) yields ~100mb savings (With FusTek and dependencies loaded).